Locale detection function that checks browser setting and lets URL parameter (locale= or lang=) override the browser setting.

Add `?locale=<localecode>` to load in a new langage.
Add `?enable=language` to enable the language selector
Or combine the two: `?enable=language&locale=<localecode>`
Still accepts a hash, but requires that the hash be a sequence of digits.

Added new locales reducer to gui:
- initializes default  react-intl/localeData
- initializes default locale messages for all locales
- default locale is ‘en’ (can be overridden by URL)

Removed dependency on react-intl-redux, added ConnectedIntlProvider (uses correct locale messages from redux based on current locale)

* Export initial states for each reducer
* combine all gui reducers (excludes scratchPaint and intl)
* combine all initial states to create default guiState for preloading in www
* expect all of the gui state to be accessible at `state.scratchGui`

- better split of hash-parser/project-loader unit tests.

The project loader that is exported with GUI just expects to be passed projectId as a prop, and it manages loading project data.

The part of the project loader that watches for URL hash changes for the playground is a new HOC that is only used in the various playground examples.

Question, should ‘x’ and ‘y’ be localizable?

- export image and sounds in dist/static/assets
- rename main export (`scratch-gui.js`, not `index.js`)
- move project-loader-hoc back to lib (VM doesn’t load properly without it)

Allow intl to be passed in to GUI as a prop (rather than having to be already in the store)

Add a jest unit test for making sure the number is rendered out when
provided and not when not provided.

firefox doesn't like comma (,) in svg path, so I change comma to space

/ht @paulkaplan

Previously we tested the ProjectLoader helper object, but now all loading is confined to storage. Unfortunately I wasn't able to get enzyme to wait for the storage promise to resolve within componentDidUpdate, so I can't test the actual results of storage.load, just what it was called with.

Add a setup file that configures the React adapter. Fix one deprecated usage for ProjectLoaderHOC tests.

There are some tests still broken, but these weren't called out by Enzyme.